1. Field of the Invention
This invention relates to a test piece that is employed in deoxyribonucleic acid (DNA) analysis and immunological analysis and to a method and apparatus for measuring the quantity of an organism-originated substance using the test piece.
2. Description of the Related Art
It is now considered possible that the human genome project for determining and analyzing all the base sequences of a human genome as huge as about 3000 Mbp will be completed sooner than the original scheduled date and determined by 2003, and the focus of the human genome project is now shifting from systematic base sequence determination to systematic function analysis.
The specific content of generic information comes down to what protein is synthesized and under what condition. With respect to the former, i.e., what protein is synthesized, methods of analysis, such as Western blotting, Northern blotting, and Southern blotting, are hitherto well known. These methods can analyze what a specific protein, DNA, and ribonucleic acid (RNA) sampled are, but are not necessarily suitable for analyzing all proteins, DNA, and RNA, extracted from a cell, at the same time.
On the other hand, regarding the latter, i.e., under what conditions protein is synthesized, the conventional methods of analysis cannot perform sufficient analysis, because protein is controlled at a transfer level. The main reason for this is that control data of both the base sequence in DNA and the corresponding contents are insufficient.
However, with the latest advancements in techniques for fixing arbitrary oligonucleotide with high density on the surface of a 1-centimeter-square carrier called a DNA chip or a DNA micro array chip, it is expected that the analysis of gene expression information will increasingly advance. The DNA chip is formed by dividing a silicon chip into a plurality of sections using photolithography and directly synthesizing single-stranded DNA having a specific base sequence on each section. As to the DNA micro array chip, a DNA macro array chip having a spot size of about 300xcexc or more previously blotted on the membrane is reduced to a spot size of about 200xcexc or less and blotted on a slide glass. The DNA chip or the DNA micro array chip is connected to a signal reader and a computer system, and it can be known which probe DNA is hybridized by the DNA disposed on the chip or the micro array chip. Depending on the DNA type disposed on the DNA chip or the DNA micro array chip and the disposition, it is possible to employ the chip or the array chip in various analyses such as DNA mutation analysis, DNA polymorphism analysis, DNA base sequence analysis, and DNA expression analysis.
The analysis employing the DNA micro array chip, however, still has quite a number of problems because discussions about array chip generation and a detector thereof have only just started. For instance, the micro array chip is made by blotting complementary DNA (cDNA) by means of a spotter, and as a method of generating the micro array chip, there is a contact printing method and a non-contact printing method. In the contact printing method, cDNA 43 is disposed on a slide glass 42 by a pin 41 in direct contact with the slide glass 42, as shown in FIG. 4A. In the non-contact printing method, cDNA 43 is blotted on the slide glass 42 by a syringe 44 in non-contact with the slide glass 42, as shown in FIG. 4B. In both the printing methods, however, there is a difference in quantity between blotted spots. Even in the best case, there is a quantity difference of 5 to 10% CV for the contact printing method and a quantity difference of 3 to 5% CV for the non-contact printing method. Further, there are sometimes defect spots and spoiled spots. For this reason, DNA varies in quantity between spots a and b on a DNA micro array chip 151, as shown in FIG. 5. DNA also varies in quantity between spot a on the DNA micro array chip 51 and spot a on a DNA micro array chip 152 generated in the same way. Because of this difference in quantity, there is a problem that the quantitative analysis of different DNAs generated from a single cell and the quantitative comparison of DNAs in the same cell differing in quantity of expression at a different time will actually include a considerable error.
To solve this problem, an improvement in the spotter was initially considered, but improvements to enhance the reproducibility of the quantity of a sample to be spotted are considered to have limits.
The present invention has been made in view of the aforementioned circumstances. Accordingly, it is the object of the present invention to provide a test piece, such as a DNA micro array chip, which is capable of performing accurate quantitative analysis even when there is a difference in quantity between blotted spots, without relying on an improvement in a spotter which enhances the reproducibility of the blotted spots.
To achieve the aforementioned object of the present invention and in accordance with one aspect of the present invention, there is provided a test piece for analyzing an organism-originated substance labeled with a second labeling substance. The test piece comprises a carrier on which a plurality of known specific binding substances differing from one another are disposed at a plurality of predetermined positions. The specific binding substances are labeled with a first labeling substance.
Since a plurality of known specific binding substances differing from one another are disposed at a plurality of predetermined positions on a carrier and labeled with a labeling substance, the quantity of a specific binding substance disposed on the test piece can be specified regardless of a difference in quantity between the specific binding substances that is caused when they are disposed on the carrier.
In accordance with another aspect of the present invention, there is provided a quantitative method comprising the steps of:
detecting a level of a first labeling signal emitted by a first labeling substance, which labels a plurality of known different specific binding substances respectively disposed at a plurality of predetermined positions on a carrier of a test piece, for each of the plurality of predetermined positions;
binding an organism-originated substance, labeled with a second labeling substance differing from the first labeling substance, to the specific binding substance and detecting a level of a second labeling signal emitted from the second labeling substance for each of the plurality of predetermined positions; and
measuring a quantity of the organism-originated substance bound to the specific binding substance, based on the detected level of the first labeling signal and the detected level of the second labeling signal.
In accordance with still another aspect of the present invention, there is provided a quantitative apparatus comprising:
first detection means for detecting a level of a first labeling signal emitted by a first labeling substance, which labels a plurality of known different specific binding substances respectively disposed at a plurality of predetermined positions on a carrier of a test piece, for each of the plurality of predetermined positions;
second detection means for detecting a level of a second labeling signal emitted by a second labeling substance, which differs from the first labeling substance and labels an organism-originated substance bound to the specific binding substance, for each of the plurality of predetermined positions; and
analyzing means for measuring a level of the organism-originated substance bound to the specific binding substance, based on the detected level of the first labeling signal and the detected level of the second labeling signal.
According to the quantitative method and the quantitative apparatus of the present invention, a level of a first labeling signal emitted by a first labeling substance, which labels a plurality of known different specific binding substances respectively disposed at a plurality of predetermined positions on a carrier of a test piece, is detected for each of the plurality of predetermined positions. An organism-originated substance, labeled with a second labeling substance differing from the first labeling substance, is bound to the specific binding substance and a level of a second labeling signal emitted by the second labeling substance is detected for each of the plurality of predetermined positions. Also, a quantity of the organism-originated substance bound to the specific binding substance is measured based on the detected level of the first labeling signal and the detected level of the second labeling signal. Therefore, it is possible to measure the quantity of the organism-originated substance independently of a difference in quantity between the specific binding substances. In addition, it becomes possible to read out the specific binding substance and the organism-originated substance disposed on the same test piece at the same time, because the labeling substance for the organism-originated substance differs from the labeling substance for the specific binding substance.
Note that if the test piece, the quantitative method, and the quantitative apparatus of the present invention are employed, an effective selection of medicine and wide utilization such as functional analysis of EST will become possible, for example, by measuring various proteins manifested according to the growth of a cancer, with the explication of the control contents and mechanism of protein synthesis being controlled at a transfer level or the realization of the measurement of a specific protein synthesized in the process of a disease, obtained from messenger RNA (mRNA) transferred within a cell.
The xe2x80x9ccarrierxe2x80x9d may be any type if a specific binding substance can be stably bound and spotted. For example, the carrier may be a membrane filter, a slide glass plate, etc. These carriers may be preprocessed to stably bind a specific binding substance.
The xe2x80x9cspecific binding substancexe2x80x9d means a substance bindable specifically with an organism-originated substance, such as hormones, a tumor marker, enzyme, an antibody, an antigen, abzyme, the other proteins, a nucleic acid, cDNA, DNA, RNA and the like. The xe2x80x9cknownxe2x80x9d varies depending on the specific binding substance. For example, in the case of a nucleic acid, the xe2x80x9cknownxe2x80x9d means that the base sequence and the base length are known, and in the case of protein, it means that the composition of the amino acid is known. Here, the specific binding substances disposed at predetermined positions on the carrier means that one kind of specific binding substance has been disposed for each position.
The xe2x80x9corganism-originated substancexe2x80x9d is a substance that specifically binds with a known specific binding substance disposed at a predetermined position on the carrier, and means, for example, substances extracted, isolated and the like from a living organism. The xe2x80x9corganism-originated substancexe2x80x9d includes substances extracted directly from a living organism and also includes these substances chemically processed and chemically modified. For instance, the xe2x80x9corganism-originated substancexe2x80x9d includes hormones, a tumor marker, enzyme, an antibody, an antigen, abzyme, the other proteins, a nucleic acid, cDNA, DNA, RNA and the like.
The specific binding substance labeled with a labeling substance (also referred to simply as a labeled specific binding substance) may be labeled at one point such as one end of stranded molecules or at a few points. If the specific binding substance has been labeled at one point, the quantity of the specific binding substance disposed at each position on the carrier is usually detectable. In the case where enhancement of detection sensitivity is desired or in the case where it is technically difficult or becomes technically complicated to label the specific binding substance at one point, the specific binding substance may be labeled at a few points.
It is preferable that the labeling substance for the organism-originated substance is different from the labeling substance for the specific binding substance. The reason for this is that a labeling signal from the labeling substance for the organism-originated substance and a labeling signal from the labeling substance for the specific binding substance can be detected independently of each other at the same time. The labeling substance for the organism-originated substance may label the organism-originated substance at one point or at a few points; although one point is preferred. The reason for this is that in the case of the organism-originated substance, there are cases where its component is not known and therefore confirmation of a method of taking a labeling substance into the organism-originated substance becomes necessary and technically complicated. Note that in the case of a known labeling substance, the organism-originated substance may be labeled at a few points similarly to the specific binding substance.
The xe2x80x9clabeling substancexe2x80x9d means a marker substance that changes either a portion of the specific binding substance or a portion of the organism-originated substance, or is added directly to these substances, in order to obtain information from these substance. The labeling substance is not particularly limited, as long as a detection signal emitted therefrom can be detected and also a rule that the labeling substance is taken into either the specific binding substance or the organism-originated substance is known in advance. For example, it is preferable to employ a fluorescent dye such as SYBR Green II(trademark), Cy5(trademark), fluorescein isothiocyanate and the like, or a radioactive isotope such as 32P, 33P and the like. The xe2x80x9clabeling signalxe2x80x9d means one emitted or output from a labeling substance. For example, the labeling signal means fluorescent light when the labeling substance is a fluorescent dye and radiation when the labeling substance is a radioactive isotope. In this case, a radioactive isotope may be employed in a specific binding substance and a fluorescent dye in an organism-originated substance, or a fluorescent dye may be employed in a specific binding substance and a radioactive isotope in an organism-originated substance. Furthermore, fluorescent dyes may be employed in both a specific binding substance and an organism-originated substance. Note that in the case where fluorescent dyes are employed in both a specific binding substance and an organism-originated substance, it is necessary to employ fluorescent dyes whose fluorescent wavelength bands do not overlap with each other. When they overlap, it is necessary to employ fluorescent dyes that do not overlap at at least a major band of detection. On the other hand, when a radioactive isotope is employed, a specific binding substance on a carrier labeled with the radioactive isotope is contacted with a photostimulable phosphor sheet and is exposed and the sheet is read by a laser, as disclosed in Japanese Patent Publication No. 5(1993)-20712 (automatic radiography of measuring a quantity of a radioactive isotope). The xe2x80x9crule that a labeling substance is taken into either a specific binding substance or an organism-originated substance is known in advancexe2x80x9d means that when the labeling substance is SYBR Green II(trademark), for example, there is a rule that it is weakly bound to single-stranded DNA or RNA and absorbed in accordance with the base length. Also, when the labeling substance is Cy5-nucleotide, there is a rule that it is taken randomly or into an end of DNA or RNA. On the other hand, a radioactive isotope such as 32P varies depending on a substance that is labeled by the radioactive isotope. For instance, when dNTP[xcex1-32P], which is employed as substrates in synthesizing cDNA from mRNA, is used, there is a rule that 32P is randomly incorporated and the amount of 32P is in proportion to the base included in the labeled nucleotide.
The xe2x80x9cbinding an organism-originated substance to the specific binding substancesxe2x80x9d means a case (hybridization) such that a stable double strand, as is viewed in DNA or RNA, is formed between complementary nucleotides and also means an extremely high specificity bond that selectively reacts only to a specific substance, such as a bond between an antigen and an antibody, a bond between biotin and avidin and the like.
The xe2x80x9cmeasuring a quantity of the organism-originated substance bound to the specific binding substance, based on the detected level of the first labeling signal and the detected level of the second labeling signalxe2x80x9d means that because the level of the first labeling signal emitted from the first labeling substance of the specific binding substance at one position on the carrier is proportional to the quantity of the specific binding substance disposed at that position, the level of the second labeling signal of the second labeling substance of the organism-originated substance bound to the specific binding substance is caused to correspond to the level of the first labeling signal, and therefore the quantity (density) of the organism-originated substance can be measured regardless of a difference in quantity between the specific binding substances. For example, consider the case where the specific binding substance is cDNA. Assume that when the number of cDNAs (specific binding substances) with one end labeled with a fluorescent dye is s at the nth position on the carrier, the quantity of fluorescent light (quantity of a labeling signal emitted from a labeling substance) is Ps. On the other hand, the number of probe DNAs (organism-oriented substances) with one end of one molecule labeled with a fluorescent dye is assumed to be c. Furthermore, assume that when the probe DNA and the nth cDNA are hybridized, the quantity of fluorescent light is Pc. It has been said that in a liquid phase system, probe DNA which is hybridized with cDNA depends on cDNA and conditions, but is about 1/100. Although it cannot be said that the case of the carrier is a perfect liquid phase system, the density m of the probe DNA is proportional at least to the number of cDNAs existing at the nth position, s. Therefore, Pc is proportional to Pc and m and the following relationship is established.
Pc∞mPs
Therefore, if Ps and Pc are measured, the density m of the organism-originated substance bound at the nth position will be obtained.
In the case where cDNA is labeled at one point, the value of Ps has no relation to the base sequence and base length of cDNA and is proportional only to the number of cDNAs disposed at the nth position. However, in the case where a labeling substance labels a specific base or labels a few points (in certain cases, tens of points) per one molecule of cDNA, the quantity of fluorescent light is varied even by the base length, and consequently, even if all the positions on a sheet of carrier indicate the same quantity of fluorescent light, it cannot be said that cDNA of the same quantity has been blotted at all the positions, because the bases of cDNA vary in length. Therefore, in this case, there is a further need to calculate xe2x80x9ca characteristic value related to cDNAxe2x80x9d. That is, a characteristic value related to cDNA, such as the base composition ratio and base length of cDNA disposed on the carrier, a quantity of fluorescent light when N cDNAs are included at one position on a carrier and the like, needs to be registered in a computer for each position. What characteristic value becomes necessary varies depending on a labeling substance employed. The fluorescence quantity Pc of probe DNA is proportional to the density m of probe cDNA and the fluorescent quantity Ps of cDNA and inversely proportional to the number of labeling substances labeling single-stranded cDNA. Therefore, the density m of probe DNA is represented by the following equation, and a characteristic value that can calculate the number of labeling substances labeling single-stranded (1 molecule) cDNA becomes necessary.
m∞Pc/Psxc3x97(number of a labeling substance labeling single-stranded cDNA)
For instance, in the case of labeling one of the 4 bases of cDNA, the number of labeled specific bases included in 1-molecule cDNA becomes necessary as a characteristic value. In the case where a labeling substance is proportional to the length of a base, the base length and the base rate at which 1 labeling substance is incorporated (i.e., how many of every of the bases 1 labeling substance is absorbed) become necessary as characteristic values.
The above and many other objects, features and advantages of the present invention will become manifest to those skilled in the art upon making reference to the following detailed description and accompanying drawings in which preferred embodiments incorporating the principle of the present invention are shown by way of illustrative example.